It's important to note that viruses don't actually want to kill their host. A dead or excessively sick host is less likely to spread the virus to the next person. So viruses generally evolve to make its host sick without killing them.

The issue is that bats have a much heartier immune system than humans do. So when a virus adapted to living in bats jumps to humans, it's waaaay too virulent for the human body. It's not that bat viruses are more likely to infect humans than a cow virus or some other animal. It's just a lot more likely to be deadly when it does.